Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session L26: Focus Session: Materials in Extremes: High-Strain-Rate Phenomena I |
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Sponsoring Units: GSCCM DCOMP DMP Chair: Dawn Flicker, Sandia National Laboratories Room: 502 |
Wednesday, March 5, 2014 8:00AM - 8:36AM |
L26.00001: Plasticity induced by pre-existing defects during high strain-rate loading Invited Speaker: Eduardo Bringa High strain-rate deformation of metals has been typically studied for perfect monocrystals. Computational advances now allow more realistic simulations of materials including defects, which lower the Hugoniot Elastic Limit, and lead to microstructures differing from the ones from perfect monocrystals. As pre-existing defects one can consider vacancy clusters, dislocation loops, grain boundaries, etc. New analysis tools allow analysis of dislocation densities and twin fractions, for both f.c.c. and b.c.c. metals. Recent results for defective single crystal Ta [Tramontina et al.., High Energy Den. Phys. 10, 9 (2014), and Ruestes et al., Scripta Mat. 68, 818 (2013)], and for polycrystalline b.c.c metals [Tang et al., Mat. Sci. Eng. A 580, 414 (2013), and Gunkelmann et al., Phys. Rev. B 86, 144111 (2012)] will be highlighted, alongside new results for nanocrystalline Cu, Ta, Fe, and Zr [Ruestes et al., Scripta Mat. 71, 9 (2014)]. This work has been carried out in collaboration with D. Tramontina, C. Ruestes, E. Millan, J. Rodriguez-Nieva, M.A. Meyers, Y. Tang, H. Urbassek, N. Gunkelmann, A. Stukowski, M. Ruda, G. Bertolino, D. Farkas, A. Caro, J. Hawreliak, B. Remington, R. Rudd, P. Erhart, R. Ravelo, T. Germann, N. Park, M. Suggit, S. Michalik, A. Higginbotham and J. Wark. [Preview Abstract] |
Wednesday, March 5, 2014 8:36AM - 8:48AM |
L26.00002: ABSTRACT WITHDRAWN |
Wednesday, March 5, 2014 8:48AM - 9:00AM |
L26.00003: Anomalous plasticity in defect-mediated phase transformations Punam Ghimire, R. Ravelo, T.C. Germann Large-scale molecular dynamics simulations of shocked wave propagation in metallic single crystals exhibit high elastic limits and are ideally suited for investigating the role defect nucleation and multiplication play on the kinetics of phase transformations. Here we report on the morphology and kinetics of shocked-induced phase transformations in Aluminum single crystals. The atomic interactions were modeled utilizing various embedded atom method (EAM) models of Aluminum, with most models exhibiting an artificial fcc$\to$bcc phase transformation in the 25-30 GPa range. For cases where plastic deformation precedes the phase transformation, anomalous defect structures atypical of plastic deformation in bcc lattices nucleate early on but anneal out with time. In all cases, the defect-mediated phase transitions proceed at faster rates than defect-free ones. [Preview Abstract] |
Wednesday, March 5, 2014 9:00AM - 9:12AM |
L26.00004: High velocity sliding at polycrystalline ductile metal interfaces J.E. Hammerberg, J.L. Milhans, R. Ravelo, T.C. Germann We present the results of large scale 3-dimensional NonEquilibrium Molecular Dynamics (NEMD) simulations for Al-Al and Al-Ta interfaces for sliding velocities in the range 20-4000 m/s at pressures of 15 GPa. System sizes include 8 M, 26 M and 138 M atoms for times to 40 ns. We discuss polycrystalline samples with initial grain sizes of 13 nm and 20 nm. For velocities above a size dependent critical velocity, v$_{c}$, the frictional force per unit area agrees with single crystal simulations. For velocities below v$_{c}$, the polycrystalline interfaces evolve to a new steady state grain size distribution characterized by very large plastic deformation with larger grain sizes, time dependent coarsening and refinement, a graded size distribution in the direction normal to the sliding interface, and significantly larger frictional forces per unit area compared to similar single crystal sliding interfaces. We also find that for the Al-Ta interface the frictional properties are determined by the weaker Al material. [Preview Abstract] |
Wednesday, March 5, 2014 9:12AM - 9:24AM |
L26.00005: A new dynamic method for determining the frictional force between ductile metals at high velocities and compressions E.N. Loomis, J.C. Cooley, J.E. Hammerberg, G.T. Gray III, C.A. Bronkhorst We present a new dynamic method for determining the frictional force between ductile metals at ns and $\mu$s time scales under shock loading conditions. The method uses laser driven plate impacts at the LANL TRIDENT Laser Facility to launch a shock wave into a target consisting of a central cylindrical plate of Be and an outer ring of Cu. The Be/Cu interface is at a 6 degree angle to the shock direction. The interface behavior is diagnosed using line-imaging velocity interferometry (line-VISAR) and surface imaging displacement interferometry (TIDI) in the region of the interface on the target rear surface (away from the impact). The TIDI diagnostic gives surface information with a 600 $\mu$m x 600 $\mu$m field of view and out of plane displacement information with 10s of nm sensitivity using gated, fast framing cameras. Using these diagnostics we extract the surface profile near the interface and from numerical continuum materials dynamics simulations determine the interfacial frictional force and its velocity and pressure dependence. [Preview Abstract] |
Wednesday, March 5, 2014 9:24AM - 9:36AM |
L26.00006: Sound speed measurements in shock compressed tantalum Robert Scharff, Paulo Rigg, Robert Hixson Shock compression experiments were performed on tantalum to determine the longitudinal sound speed on the Hugoniot from 36 to 105~GPa. Tantalum samples were impacted directly on to lithium fluoride windows at velocities ranging from 2.5 to 5.0~km/s and the resulting particle velocity profiles at the sample/window interface were recorded using optical velocimetry techniques. The time of arrival of the rarefaction wave from the back surface of the tantalum sample was then used to determine the longitudinal sound speed at the corresponding impact stress. In contrast to recently reported work, we see no evidence of a phase transition in the tantalum in this stress range. [Preview Abstract] |
Wednesday, March 5, 2014 9:36AM - 9:48AM |
L26.00007: ABSTRACT WITHDRAWN |
Wednesday, March 5, 2014 9:48AM - 10:24AM |
L26.00008: Plastic flow and lattice dynamics experiments on shock and ramp loaded solid-state samples at extreme pressures and strain rates Invited Speaker: Bruce Remington Experiments are being done on high power lasers, such as the Omega laser at LLE and the Janus and NIF lasers at LLNL, to probe the solid-state plastic response of materials to high pressure (50-500 GPa), and very high strain rate deformation (1.e6 - 1.e10 1/s). Two classes of experiments will be described. Dynamic Laue diffraction experiments with a time resolution of $\sim$0.1 ns have been developed to probe the microscopic lattice response of single crystal samples to a strong shock. In particular, the time scale for the onset of plasticity and the rate of the 1D to 3D lattice relaxation are a direct measure of how rapidly dislocations can be generated and transported on sub-nanosecond time scales (lattice kinetics). Macroscopic plastic flows at high pressure and strain rate can be generated that span a few tens of nanoseconds by using the Rayleigh-Taylor or Richtmyer-Meshkov fluid instabilities. Results from both classes of experiments will be compared with simulations using various models of flow stress (strength), a multi-scale model for bcc strength, and with analytic theory, where possible. [Preview Abstract] |
Wednesday, March 5, 2014 10:24AM - 10:36AM |
L26.00009: A Backward Characteristics Method for Impact Test Haibo Xu, Hao Pan The laser velocity interferometer has becoming an important method to study the dynamic response of materials under shock loading. A backward characteristics method considers the interaction between incident waves and reflects waves. This method can give more reasonable analysis results from the interface/freesurface velocity of the sample under test. The mechanical variables under adiabatic releasing can be obtained. Comparing with the simulationof the impact test of Tantalum, the sound speed vs. particle velocity, stress vs. Volume strain calculated by the backward characteristics method are according with the results gived by the hydrodynamics code. The backward characteristics method is used to analysis the reverse impact tests of Tin and more wealthy and important information about phase transiton under shock loading, yield strength and adiabatic releasing path is obtained. [Preview Abstract] |
Wednesday, March 5, 2014 10:36AM - 10:48AM |
L26.00010: The effect of moisture content on the dynamic fragmentation of wet sand at high strain rates Kun Xue A comprehensive model is established to account for the instability onset of rapidly expanding granular shells subject to the explosion loadings generated by the detonation of the central explosives. The moisture content strongly influences the shock interactions in the wet particle beds and the ensuing evolvement of the granular compacts. A material model for granular materials which can account for the degree of saturation was incorporated into a non-linear dynamic simulation program to investigate the moisture of effect on the shock responses of wet granular materials. In conjunction with our instability model, the predicted instability diameters of the expanding dry/wet granular shells are in a good agreement with the experimental results. Particularly the postponed instability onset of the wet granular shell found both experimentally and analytically can largely be attributed to the significantly greater kinetic energy obtained by wet particles thanks to less energy of shock wave consumed in compacting the granular materials. [Preview Abstract] |
Wednesday, March 5, 2014 10:48AM - 11:00AM |
L26.00011: ABSTRACT WITHDRAWN |
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